chore(package): update sinon to version 7.3.2

Closes #6

Author: greenkeeper[bot]

Diff for: package.json

@@ -55,7 +55,7 @@
     "mocha": "^5.0.1",
     "nyc": "^11.4.1",
     "rimraf": "^2.6.2",
-    "sinon": "^5.0.0"
+    "sinon": "^7.3.2"
   },
   "nyc": {
     "sourceMap": false,